The investigators aim to better characterize factors that contribute to fracture in boys and girls and to assess whether such factors track across a four year period. The innovation is to use novel methods and an integrated approach, to measure the influence of risk-taking behaviour, body composition, bone microstructure, motor proficiency, diet and physical activity in one model across growth. This will provide a more comprehensive picture of the key multi-factorial predictors of fracture within- and between-sexes. This essential information will provide the basis for change in public health policy, clinical practice, community programs, and targeted interventions.